British Patent 887,900 and U.S. Pat. No. 3,256,140 teach the usefulness of various quaternary aminomethyl substituted acrylamide polymers for several purposes in the manufacture of paper. These references show the preparation of such polymers by the homopolymerization or copolymerization of monomeric quaternary aminomethyl substituted acrylamide or methacrylamide. This process requires the preparation and isolation of the expensive quaternary monomer and does not lend itself to commercial practice. Further, the quaternary monomer does not lend itself to the preparation of the relatively high molecular weight acrylamide polymers, which have been found desirable for use as flocculating agents.
U.S. Pat. No. 3,859,212 teaches that certain acrylamide polymers containing aminomethyl groups have desirable properties as flocculating agents and are rendered more stable by converting the aminomethyl groups to the quaternary form. However, it has been found that the methods for preparing the polyquaternary ammonium compounds, as taught in the prior art, are not adapted to commercialization. Thus, for example, when quaternization was attempted at practical concentrations of polymer in an alkaline aqueous medium the polymer formed a thick gel prior to completion of the quaternization reaction, said gel being so viscous as to render it difficult or impossible to apply same as a flocculating agent or paper treating chemical. On the other hand, when it was attempted to carry out the reaction at an acidic pH in aqueous medium it was found that the reaction proceeded so slowly that little or no product could be obtained within a reasonable time.
It would therefore be desirable and is an object of the present invention to provide a method for preparing quaternary ammonium derivatives of acrylamide polymers rapidly and in good yield.